Break up the model module

The `model` module has historically been one giant module re-exporting
all of the model types, which is somewhere around 100 types. This can be
a lot to look at for a new user and somewhat overwhelming, especially
with a large number of fine-grained imports from the module.

The module is now neatly split up into submodules, mostly like it has
been internally since the early versions of the library. The submodules
are:

- application
- channel
- error
- event
- gateway
- guild
- id
- invite
- misc
- permissions
- prelude
- user
- voice
- webhook

Each submodule contains types that are "owned" by the module. For
example, the `guild` submodule contains, but not limited to, Emoji,
AuditLogsEntry, Role, and Member. `channel` contains, but not limited
to, Attachment, Embed, Message, and Reaction.

Upgrade path:

Instead of glob importing the models via `use serenity::model::*;`,
instead glob import via the prelude:

```rust
use serenity::model::prelude::*;
```

Instead of importing from the root model module:

```rust
use serenity::model::{Guild, Message, OnlineStatus, Role, User};
```

instead import from the submodules like so:

```rust
use serenity::model::channel::Message;
use serenity::model::guild::{Guild, Role};
use serenity::model::user::{OnlineStatus, User};
```

1 files changed, 5 insertions, 2 deletions

diff --git a/src/utils/colour.rs b/src/utils/colour.rs
index 4e612cc..c59f4be 100644
--- a/src/utils/colour.rs
+++ b/src/utils/colour.rs
@@ -28,8 +28,9 @@ macro_rules! colour {
 /// via [`g`]:
 ///
 /// ```rust
-/// # use serenity::model::{Role, RoleId, permissions};
-/// use serenity::utils::Colour;
+/// # use serenity::model::guild::Role;
+/// # use serenity::model::id::RoleId;
+/// # use serenity::model::permissions;
 /// #
 /// # let role = Role {
 /// #     colour: Colour::blurple(),
@@ -41,6 +42,8 @@ macro_rules! colour {
 /// #     permissions: permissions::PRESET_GENERAL,
 /// #     position: 7,
 /// # };
+/// #
+/// use serenity::utils::Colour;
 ///
 /// // assuming a `role` has already been bound
 ///